Quote:
Originally Posted by carguy138
I have no experience in what you suggested but I don't know how good of an idea that is. For two reasons I wouldn't do that.
1) These cars have a lot of interwoven control modules and electrical systems.
2) Brake system may be involved.
Another thing that I was thinking about (and if anyone knows more, please correct me) but the portion that powers the rear wheels on a xdrive is much different than the rear wheel drive. I now believe a second clutch pack connects the transmission to the rear driveshaft as well as a clutch pack to the front drive shaft. When the front drive shaft is removed, the clutch pack to the rear is locked since the ECU believes the front wheels have zero grip. I do not know the answer to this but that may cause issues down the line. Evidence of a clutch pack for the rear driveshaft is shown in the video on here. With the ability to send up to 100% of power to the front tires, there would have to be a way to disable the rear.
http://www.awdwiki.com/en/xdrive/
Long story short, this car is complicated enough and if there was a simple way to modify the drive train easily, it would have likely been done by now. Problem is with experimenting is that now you have the potential to break very expensive parts that aren't easily accessible.
Now that there is a chance that the transmission isn't directly bolted to the rear driveshaft on a 6mt, I'd tread very lightly on this matter.
EDITED: I might be wrong per a wiki article that I just read. Check out the last sentence, it states that the rear drive shaft is hard coupled to the transmission output.
https://en.wikipedia.org/wiki/BMW_xDrive
"Instead of a permanent torque split (which is featured in earlier systems), xDrive provides variable torque split between the front and rear axles through the use of a multi-plate wet clutch located in the gearbox on the output to the front drive shaft. This setup allows xDrive to modulate the torque split between the front and the rear axles, which is normally split at 40:60 ratio, respectively. If wheel slip is detected by the ABS/DSC system, xDrive can react within a tenth of a second to redistribute up to 100% of the engine power to the front or rear axle.[1] The wet clutch is applied through a high speed electric servo motor turning a cam-shaped actuator disc. As the rear drive shaft is hard-coupled to the transmission output, full torque transfer to the front axle can only be achieved if the rear wheels have no traction and are both slipping." |
I need to be able to switch from AWD to RWD on demand. I do drag race and my present setup causes me to have 4 wheels spins at the start line. My idea would be to set the car for RWD, do a quick burnout to preheat the tires for better traction, then put back the car in AWD just before the race.
I must have a way to do that without pulling the driveshaft obviously. Have you found other options in the DSC module that might be related?
Do you think that If I find a way to code the option live at the track my rear tires would both spin for a burnout? I can do coding and I could also automate it.